Conventional bicycles have long used caliper brakes. A typical prior art cantilever brake assembly comprises an upper brake cable attached to the operating hand, a lower brake cable attached to a pivotal actuating seat, a shoe and a packing. When the upper brake cable is pulled by the handle, the lower cable will also be pulled upwards. Hence, the actuating seat will be pulled to turn about a pin thereby forcing the shoe to press on the rim of the bicycle wheel.
Both center-pull and side-pull caliper brakes (e.g., position of the pivot) are known. Each type has encountered problems in that these tend to give an extremely mushy reaction during operation due to excessive flexing of the brake arms. Another problem has been that caliper type brakes have not afforded independent adjustment of the return spring force on each side of the rim.
There is yet another problem with brake shoe centering in caliper type brakes. Normally, the braking surfaces of the brake shoes are in parallel to the plane of the wheel but not to the arc of the wheel rim. The brake arms and the brake shoes are likely to deflect in the direction of rotation of the wheel rim when the braking surfaces are brought into contact with the wheel rim to apply a braking force. Such deflection causes the forward end of the braking surface, in the direction of rotation of the wheel rim, to separate from the wheel rim. On the other hand, the rear end of the braking surface comes into hard contact with the wheel rim. This results in uneven engagement of the braking surface with the wheel rim or in an improper application of the braking force. Also, the braking surface of the shoe body is unevenly worn to a considerable extent and is highly subject to damage.
An additional problem is that of obtaining adjustment of the brake shoe radially for alignment with the tire rim, rotationally along the axis of the brake caliper, and rotationally along the axis perpendicular to the caliper and to the plane of the tire. Also, inward adjustment toward the rim may be needed as the brake pad wears.
Various attempts at providing an adjustable brake shoe assembly have been made. In general, such attempts include "beefing up" and strengthening the various parts adding additional weight to the bicycle. Redundant clamps have also been used. Recently, the TEKTRO Technology Corporation of Taiwan, Republic of China, has marketed a brake assembly model 866A in which the rod on which the brake shoe is mounted is located in a ring having a rounded exterior. The ring is held in an "eye bolt" which is clamped to the brake lever. The "eye bolt" comprises a toroidal head and a threaded leg by which it is attached to the brake lever. The inner surface of the "eye" or head is curved to conforming to the outer surface of the ring thereby simulating a ball joint providing a degree of universal movement. The eye bolt is secured to the brake lever by having the threaded leg pass through the hole and securing a nut on the leg against the back surface of the lever. The problems with this construction are that upon tightening the nut, the single leg of the "eye bolt" is subjected to considerable torque so that the selected adjusted position of the shoe cannot be fixed during assembly. Similarly, during use the "eye bolt" is subjected to vibration and to the braking force of the brake shoe itself thereby causing a torque to be applied to the single nut. Consequently, the "eye bolt" will turn out of desired alignment. Furthermore, compression about the ring is not even or balanced as the "eye", when clamped, is elliptically distorted. As a result of all of this, effective, efficient and secure adjustment is not obtained.
The present invention overcomes these disadvantages inherent in the above-described prior art bicycle braking assemblies while also providing a cantilever braking assembly which is light in weight, inexpensive to manufacture, provides good braking and enables easy angular adjustment of a braking surface of a shoe body relative to a wheel rim, and easy adjustment of a clearance between the wheel rim and the brake shoe.
It is an object of the present invention to provide a cantilever brake assembly having an adjustable shoe mounting structure which facilitates the adjusting operation while ensuring a wide range of adjustments.
It is another object of the present invention is to further expand the freedom in adjusting the position or orientation of the brake shoe.
It is still another object of the present invention is to ensure reliable fixation of the brake shoes after positional adjustment.
It is still another object of the present invention to provide a cantilever brake assembly for a bicycle which is easy to assemble.
It is a further object of the present invention to provide a cantilever brake assembly for a bicycle which is simple in construction.
It is a further object of the present invention to provide a braking assembly for a bicycle which is economical to manufacture.